The sunrise time you read in your local newspaper was most likely provided by the U.S. Naval Observatory. Astronomers there calculate sunrise times using the standard laws of planetary motion set down by Isaac Newton and modified by Albert Einstein, plus recent daily observations of the sun.
The calculations are based on the sun’s coming over a level horizon, so objects like mountains and skyscrapers can delay the time you actually see the sun’s rays. What’s more, the U.S. Naval Observatory assumes sea level as the height of all cities, since differences in the elevations of cities don’t change the calculations much.
But the width of a large city could be a factor. All else being equal, the east side of a city could see the sun a minute or two earlier than the west side. The U.S. Naval Observatory looks at only one sunrise point for each city. These points are calculated using population maps prepared by the Census Bureau.
I am looking for a builting site that would be suitable for a vastu home. One of the primary factors in determining the suitability of a site is the delay of sunrise on the site which is limited to 12 min. That time is going to vary throughout the year depending on the angle of the rising sun and whether or not there are obatacles such as mountains. It should be possible, using some topo software to check the area 23 degrees North and South of due East for obstacles and calculate the delay of sunrise pretty closely for any proposed site. Does anyone have any information on how to accomplish this?
Tim,
Do you want the time of sunrise and the azimuth point of the rising sun? Check out the US Naval Observatory at http://aa.usno.navy.mil/data/docs/mrst.php
Bruce